Electrical circuit breakers



Nqv. l, 1960 1.. w. BRACKETT 2,958,749

ELECTRICAL CIRCUIT BREAKERS Filed March 13. 1958 In 0 entor L auzrence WB T'd c/(eii By his Attorney MM 41/ $40 United States Patent 2,95 8,749-ELECTRICAL 'CIR-CUIT BREAKERS Lawrence W. Brackett, Georgetown, Mass.,assignor, by mesne assignments, to Wood Electric Corporation, acorporation of Massachusetts Filed Mar. 13, 1958, Ser. No. 721,134 4Claims. (Cl. 200-116) The present invention relates to improvements inelectrical circuit breakers, particularly of the trip-free type and isherein illustrated as embodied in a highly compact construction for abreaker more fully disclosed in United States Letters Patent No.2,613,296, granted June 24, 1949, upon application of Morris B. Wood.

In the circuit breaker of the prior patent one movable contact actuatedby a lengthwise sliding button is provided to cooperate with a singlefixed contact in opening the circuit running through the contacts and athermostatic latch is arranged to release a circuit-retaining memberwhenever an excessive current flows for a sufficient period of time toheat the latch above a releasing temperature. The circuit breaker of theprior patent is extremely compact and efliciently designed to provideeffective trip-free operation even under conditions of high amplitudesustained vibrations and low temperatures commonly experienced in theaeronautical field.

An object of the present invention is to so improve the construction andarrangement of parts in the prior push button circuit breaker that,without increasing the external dimensions it is possible to provide adouble break in a circuit to be controlled through the use of two setsof fixed and movable contacts, in place of the single set previouslyused and in addition to enable an instantaneous trip of the retainingmember as well as the time delay trip of the prior breaker. In this waythe range of protection afforded by the improved breaker is increasedwhile maintaining and in some respects improving the minimum spacerequirements for insulation and surface leakage. Accordingly, thepresent invention proposes the provision of a split rectangular framefor a circuit breaker formed with a hollow shell and a relatively flatcover plate therefor, in which shell is disposed the two fixed contacts,a bridging bar including movable contacts for engagement with the fixedcontacts, a pair of movable cam members, a manually operable wedgingmember between the cam members, a thermostatic latch for locking one cammember, a lengthwise slidable push button connected to operate thewedging member, a slide for carrying the bridging bar, in which frame isalso formed a two-part of the guideway at right angles to the length ofthe push button, one part guideway being on the shell and the other partbeing on the cover plate, so that the slide is always maintained in aposition with the bridging bar in alinement with the fixed contacts anda novel form of magnetic trip to provide both a delayed trip and aninstantaneous magnetic trip. Preferably, for the purpose of savingspace, the bridging bar and the thermostatic latch are disposed inparallel relation along opposite sides of the rectangular frame, withthe guideway between them, and also are disposed at right angles to thebridging bar, the thermostatic latch and the push button regardless ofwhether a magnetic trip is employed or not.

These and other features of the invention, as hereinafter described andclaimed, will be apparent from the following detailed specification,taken in connection with the accompanying drawings, in which:

2,958,749 Patented Nov. 1, 1960 Fig. 1 is a sectional side view of acircuit breaker embodying the features of the present invention;

Fig. 2 is a sectional end view taken along the line II-II in Fig. l andillustrating the cover on the shell of the frame;

Fig. 3 is a sectional detail view of a guideway for a contact bridgingbar slide in the breaker of Fig. 1 as seen in the direction of thearrows on the line IIIIII of that figure; and

Fig. 4 is a further sectional detail View taken along the line IVIV ofFig. 1.

The trip-free overload circuit breaker illustrated in the drawings ismanually operated to close or open a circuit to be controlled and isactuated automatically to open and to hold open the circuit underconditions of excessive current flow regardless of any manual operationof the breaker. The breaker comprises a split rectangular frame formedwith a hollow shell 2 and a matching cover plate 4 held to the shell byrivets 6. All of the operating parts are contained in operating relationwithin the shell part of the frame, so that before the cover is appliedthe functioning of the breaker may be tested and adjusted.

As in the overload circuit breaker of the prior patent above identified,the illustrated breaker has a fixed contact and a movable contact toengage the fixed contact and to close a circuit to be protected,together with a pair of cam members one of which is connected to themovable contact and the other of which is engaged by a thermostaticlatch, for locking the latter cam member against movement away from thecontact connected one to enable manual operation of the contacts to openand close the connected circuit. To enable manual operation the contactconnected cam member is yieldingly moved toward the locked cam member toopen the circuit and is separated from the locked cam member by awedging member to close the circuit, as in the prior breaker, thecontact operating cam member being formed as a bulge in a leaf spring tosupport the movable contact and to provide a yielding force to open thecontacts. Due to the space restrictions and to the necessity for anability to withstand vibration in this type of electrical apparatus,while retaining the usual requirements for convenient assembly, testingand adjustability, it has been difficult, if not impossible heretoforeto provide a satisfactory arrangement of double break contacts in such acircuit breaker.

In the embodiment of the present invention the dithculties met inassembly, testing and adjustment of a double break circuit breaker areavoided by mounting a pair of fixed contacts 3 and it} in the shell 2 ofthe breaker frame and by providing a bridging bar 12 for the movablecontacts mounted on a slide 14, the guideway for which is formed in twoparts. One part 16 (see Fig. 3) of the guideway is formed on the shell 2and the other part 18 is formed on the cover plate 4. By so doing theparts of the breaker may be assembled and held in assembled relation fortesting and adjustment purposes with a half cover plate for securing thebridging bar slide in position while a thermostatic latch 2@ for holdingthe contacts closed is exposed for easy accessibility, testing andadjustment and is disposed in a lengthwise position parallel to one sideof the shell. The bridging bar is also arranged parallel to thethermostatic latch along the opposite side of the shell from the latch,while the guideway for the slide 14 is located at right angles to boththe bridging bar and the latch and is disposed between them.

rise the movements of the bridging bar and its slide are directed in apath alined with the fixed contacts, the slide being disposed formovement at right angles to the movement of the wedging member, so thata most efficient transfer of motion is obtainable between the parts.

The wedging member is in the form of a set of rolls 22 connected to alink '23, in turn pivotally connected to a lama,

manually operable cylindrical insulating button 24. The button isslidable in a metal sleeve 26 arranged at right angles to the guidewayl6, 18 for the bridging bar slide and is disposed between the bridgingbar and the thermostatic latch, The sleeve 26 is fixed to the shell partof the frame so that it maintains its proper relationship with the slideeven when the cover plate 4 is removed.

To retain the button 24 against rotation in the sleeve 26 the link 23 ismade in two parts, as shown in Fig. 2, one part being pivotallyconnected to the button by a pin 28 projecting from either side of thebutton, the link parts being disposed to slide in shallow recesses inthe shell 2 and the cover plate 4. To hold the link 23 in alinement withthe button, so that the pressure applied to the button will act directlyon the link, the parts of the link are connected together at theirmidpoints by a stud 30 which passes beneath the inner end of the buttonand forms a stop for the link when the wedging rolls 22 are pressed bythe locked cam member, indicated at '32, the contact connected cammember being indicated at 3'3 and shown as being fixed'to one end of theslide 14. The stud 3t also prevents application of excessive pressure onthe bridging bar and contacts. For insuring that the link remains inalinement with the button during manual operation of the breaker, and ingenerally parallel relation to the bridging bar and thermostatic latch,the locked cam member 32 is pressed yieldingly against the wedging rolls22 by a spring 34 stretched between the cam member 32 and a pin 36supported at its ends in openings formed in the side of the shell 2 andin the cover plate 4. The cam member 32 is rotatably mounted at itslower end on a pivot 38 passing through a loose fitting slot 40 in thecam member 32.

Whenever the circuit through the breaker is opened automatically by anoverload current flow the wedging rolls 22 move with the cam member 32to release the bridging bar 12 from contact-making position, thebridging bar being actuated for this purpose by a spring 42 compressedbetween the left end of a recess 44 in the frame shell 2 and a reducedprojection of the slide at the opposite side of the bridging bar fromthe main body of the slide. The spring 42 is constructed with greaterstiffness than the spring 34 acting on the cam member 32 so that aprompt opening of the circuit is insured when the locked cam member isunlocked.

The thermostatic latch 26 is similar to that disclosed in the priorpatent, above referred to, and comprises a reversely bent bimetallicstrip secured at one end to a terminal plate 46. The other end of thebimetallic strip has riveted to it a latch plate 48 and a magneticarmature 50. The terminal plate 48 is secured in place within the shell2 of the breaker frame by a pair of screws 52 and 54 threaded throughthe terminal plate and disposed in loose fitting openings in the endwall of the shell 2, one extremity of the plate protruding from thebottom wall of the shell opposite the button 24 and supporting aconnection clamping screw 56. The screw 54 serves to retain the terminalplate in place and the screw 52 to adjust the locking position of thelatch 22 and for calibration purposes after assembly of the parts.

The thermostatic latch 2% acts to open the circuit through the breakerby flexing as overload currents flow through the latch, deflecting itfrom its cold position. To assist in unlocking the cam member 32 whenextremely high or short circuit currents flow through the thermostaticlatch the magnetic arrnature 50 is located close to a half-turn magnetcore 58 (see Fig. 4) surrounding three sides of the terminal plate 4-6and being located within attracting distance of the core 58. The core 58is U-shaped and has a central opening through which the retaining screw54 passes to hold both the terminal plate and the magnetic core inplace.

The current entering the breaker by the terminal plate 46 flows throughthe thermostatic latch 20, a flexible lead 60, to an L-shaped contactsupporting plate 62.

The fixed contact is secured to the end of the contact plate oppositethe flexible lead, the current passing from the contact 10 into thebridging bar 12 and a current carrying shunt lead 63 running between theends of the bridging bar. From the bridging bar 12 the current flows tothe other fixed contact 8 and out of the breaker through a secondterminal plate 64.- to which the fixed contact 8 is secured. Theterminal plate n4 is retained in the shell 2 by frictional engagementwith a slot formation fitting closely with the shape of the plate 64 andalso protrudes through the end wall of the shell, opposite the button24, there being a connection clamping screw 66 in the exposed end of theterminal plate 64.

The nature and scope of the invention having been indicated and aparticular embodiment having been described, what is claimed is:

l. A double break trip-free overload circuit breaiker having a splitrectangular frame formed with a hollow shell and a cover plate, a pairof fixed contacts in the shell, a bridging bar for connecting the fixedcontacts, a pair of movable cam members, a wedging member acting betweenthe cam members to separate them, resilient means for moving the cammembers together, a thermostatic latch for locking one of the cammembers against movement away from the other, a lengthwise slidable pushbutton connected to the wedging member and a slide on which the bridgingbar is mounted and to which the other cam member is connected formovement toward and from the fixed contacts to open and close thecircuit therethrough, in combination with a two-part guideway for theslide, one part of which is formed on the hollow shell, the other partof which is formed on the cover plate and both of which extend at rightangles to the length of the push button to maintain the bridging bar inits movements with the slide in alinement with the fixed contacts,terminal plates connected to one of the contacts and to the thermostaticlatch, a magnetic core secured to the frame in surrounding relation tothe latch connected plate and an armature secured to the latch withinattracting distance of the core to provide both a delayed trip byheating of the latch and an instantaneous trip by magnetic attraction ofthe core.

2. A double break trip-free circuit breaker having a split rectangularframe formed with a hollow shell and a cover plate, a pair of fixedcontacts in the shell, a bridging bar for connecting the fixed contacts,a pair of movable cam members, a wedging member act-ing be tween the cammembers to separate them, resilient means for moving the cam memberstogether, a thermostatic latch for locking one of the cam membersagainst movement away from the other, and a slide on which the bridgingbar is mounted and to which the other cam member is connected formovement toward and from the fixed contacts to open and close thecircuit therethrough, in combination with a twopart guideway for theslide, one part of which is formed on the hollow shell and the otherpart of which is formed on the cover plate to maintain the bridging barduring its movements with the slide in alinement with the fixedcontacts, the bridging bar and the thermostatic latch being disposedlengthwise in parallel relation along opposite sides of the shell withthe guideway for the slide being located between them and disposed atright angles to the bridging bar and the thermostatic latch and amanually operable push button slidingly mounted in the frame formovement in a lengthwise direction between and parallel to the bridgingbar and the thermostatic latch.

3. A double break trip-free circuit breaker having a split rectangularframe formed with a hollow shell and a cover plate, a pair of fixedcontacts in the shell, a bridging bar for connecting the fixed contacts,a pair of movable cam members, a manually operable wedging member actingbetween the cam members to separate them, resilient means for moving thecam members together, a thermostatic latch tor locking one of the cammembe s against movement away from the other, and a slide on which thebridging bar is mounted and to which the other cam member is connectedfor movement toward and from the fixed contacts to open and close thecircuit therethrough, in combination with a two-part guideway for theslide, one part of which is formed on the hollow shell and the otherpart of which is formed on the cover plate to maintain the bridging barduring its movements with the slide in alinement with the fixedcontacts, the bridging bar and the thermostatic latch being disposedlengthwise in parallel relation along opposite sides of the frame withthe guideway for the slide between them, the wedging member being in theform of a plurality of rolls, a link connected at one end to the rollsand a button connected to the other end of the link and slidinglymounted on the shell between the bridging bar and the thermostatic latchin parallel relation to the bar and latch.

4. A double break trip-free circuit breaker having a split rectangularframe formed with a hollow shell and a cover plate, a pair of fixedcontacts in the shell, a bridging bar for connecting the fixed contacts,a pair of movable cam members, a manually operable wedging memher actingbetween the cam members to separate them, resilient means for moving thecam members together, a thermostatic latch for locking one of the cammembers against movement away from the other, and a slide on which thebridging bar is mounted and to which the other cam member is connectedfor movement toward and from the fixed contacts to open and close thecircuit therethrough, in combination with a two-part guideway for theslide, one part of which is formed on the hollow shell and the otherpart of which is formed on the cover plate to maintain the bridging barduring its movements with the slide in alinement with the fixedcontacts, the bridging bar and the thermostatic latch being disposedlengthwise in parallel relation along opposite sides of the frame withthe guideway for the slide between them, the wedging member being in theform of a plurality of rolls, a link connected at one end to the rolls,a button connected to the other end of the link and slidingly mounted inthe frame between the bridging bar and the thermostatic latch inparallel relation to the bar and latch, terminal plates secured in theframe to the same opposite sides along which the bridging bar and thethermostatic latch are disposed, said terminal plates protruding throughthe end of the frame opposite the button, a half-turn magnetic coresecured to the frame in surrounding relation to the terminal plate atthe side of the flame with the thermostatic latch and an armature platesecured to the latch within attracting distance of the core to provideboth a delayed trip by heating the latch and an instantaneous trip bymagnetic attraction of the core.

References Cited in the file of this patent UNITED STATES PATENTS2,166,545 Getchell July 18, 1939 2,287,875 Grober June 30, 19422,611,055 Webster Sept. 16, 1952 2,613,296 Wood Oct. 7, 1952 2,660,642Warren Nov. 24, 1953 2,668,212 Schleicher Feb. 2, 1954 2,813,168Mascioli et al. Nov. 12, 1957 2,833,888 Bessiere May 6, 1958

